Master slide object automatically arranged on top of foreground slide

I have over 200 slides and would like to get rid of a few objects which are all positioned in the same positions for each slide.

These objects are not a part of the template master, so it is necessary to go through each slide.

I'm thinking that I can cover them with a coloured square using the master slide template, however I am having trouble applying the slide so that the square I created sits on the top layer automatically (in order to cover the undesirable objects without manual input).

Any ideas?